Device for discharging cellulosic pulp from a digester

ABSTRACT

At least three sets of scraper devices are inserted in the bottom of a continuous cellulose digester for forwarding pulp passing along the axis of the digester and within a partition therein through a first discharge outlet, and pulp passing along the shell of the digester and outside said partition through a second discharge outlet. Each scraper device comprises a radially directed inclined shaft extending through the digester shell and said partition, said shaft carrying scraper arms sweeping the inside of a calotte-shaped portion of said partition as well as scraper arms sweeping the inside of a hemispherical bottom portion of the digester shell.

ite States Patentv 11 1 1111 3,787,284

Richter 1 Jan. 22, 1974 1 DEVICE FOR DISCHARGING CELLULOSIC 3,222,141 12/1965 Donaldson 221/2905 PULP FROM A DIGESTER 3,475,271

Inventor: Johan C. F. C. Richter, St. Jean Cap Ferrat, France Assignee: Kamyr Aktiebolag, Karlstad,

Sweden Filed: June 19, 1972 Appl. No.: 264,240

Foreign Application Priority Data June 22, 1971 Sweden.. 8073/71 References Cited UNITED STATES PATENTS Richter 162/246 10/1969 Laakso 162/246 X Primary Examiner-S. Leon Bashore Assistant Examiner-Richard V. Fisher Attorney, Agent, or Firm-Cushman, Darby & Cushman ABSTRACT At least three sets of scraper devices are inserted in the bottom of a continuous cellulose digester for forwarding pulp passing along the axis of the digester and within a partition therein through a first discharge out-' let, and pulp passing along the shell of the digester and outside said partition through a se conddischarge out- "let. Each scraper device comprises a radially directed inclined shaft extending through the digester shell and said partition, said shaft carrying scraper arms sweeping the inside of a calotte-shaped portion of said partition as well as scraper arms sweeping the inside of a hemispherical bottom portion of the digester shell.

2 Claims, 2 Drawing Figures PATENTEU JAN 2 21974 SHEET 1 [IF 2 DEVICE FOR DISCHARGING CELLULOSIC PULP FROM A DIGESTER The invention relates to a device for discharging of cellulosic pulp from the lower end of a digester provided with a partition which is concentric to the digester shell and'which separates a central zone from a peripheral zone of the digester cross-section, and in which digester the space inside said partition communicates with a first pulp outlet and the space between the partition and the digester shell communicates with a second pulp outlet. i

In a discharging device of the type which has become known from the US. Pat. No. 3,579,421, two independently rotatable scraper devices are situated at the bottom of the digester and designed for discharging the pulp from each zone out through a separate outlet. The scraper devices are driven by shafts extending in the axial direction of the substantially cylindrical digester, said shafts being coaxial and one of them forming a sleeve surrounding the other shaft. This arrangement of the scraper devices involves constructional difficulties with respect to the operation as well as the bearing and sealingof the concentric drive shafts, and furthermore the central location thereof requires that the pulp outlets have to be placed eccentrically in the digester bottom. It is also difficult to insert from below in the digester a central supply tube for washing liquid or similar materials which many times may be desirable.

According to the invention the above-mentioned difficulties are eliminated and a simple scraper arrangement is obtained by a development of such inclined scrapers as have become known from the Swedish patent specification'No. 326,095 (U.S. patent application Ser. No. 245,167 copending herewith).

The essentially characterizing feature of the invention consists in that rotary scraper means active inside the partition are attached to a radial, outwardly and downwardly directed shaft extending through the digester shell as well as through the partition, said shaft also carrying scraper means active in the space be-v tween the partition and the digester shell. The operation of the central and the peripheral scraper by means of a common shaft involves a considerable simplification of the bearing and sealing problems, even when considering that for sweeping over a sufficiently great part of the bottom surface usually at least three double sets of scrapers are required, one drive shaft being provided for each set. i

The discharging device of the invention will be further described herein below with reference to the accompanying drawings in which:

FIG. 1 diagrammatically shows a vertical and axial cross-section of the lower part of a continuous cellulose digester provided with the discharging device of the present invention; and

FIG. 2 is a top plan view along the line IIII of FIG. 1. 1 v

The shown digester is of the type wherein it is desirable to separate the shell pulp, that during the continuous passage of the pulp in the longitudinal direction of the digester has moved close to the cylindrical shell ll of the digester, from the core pulp that has moved closer to the axis of the digester and formed a central core in the continuously descending pulp column. The shell pulp and the core pulp" usually are of different qualities, for instance on account of different treatment or different'starting material. In order to separate the two pulp kinds in connection with their discharge from the digester, the digester is provided with a first outlet 13 communicating with the peripheral zone B of a cross-section of the lower-most portion of the digester, and with a second outlet 15 communicating At the level where the shell 11 merges into the spherical bottom portion 17 the two kinds of pulps in the zones A and B are separated from each other during their descent on opposite sides of the uppermost, preferably pointed edge of the stationary partition 23 inserted in the'lower end of the digester. This partition is calotte-shaped and is concentric to the spherical portion 17 of the'digester shell but is of a smaller radius, so that between the partition 23 and the digester shell 17 there is formed an annular space 25 of uniform width. The calotte'shaped partition 23 is joined to a cylindrical centrally located neck 27. The horizontally directed outlet 15 is connected to said neck via an inclined conduit 29 penetrating the bottom 21.

The movement into the necks l9 and 27 of pulp that has passed outside and inside the partition 23 is assisted by three or more scraper devices which are placed eccentrically in the digester bottom portion and in positions symmetrical about the axis of the digester. Each scraper device includes a shaft 33 driven by a motor 31 and extending through the spherical part 17 of the digester bottom as well as through the partition 23. This shaft carries a first set of scraper means 35 operating in the space 25 and a second set of scraper means 37 operating in the central space inside the partition 23. The scraper means of each set may consist of two or more radially directed or curved arms connected to the shaft. The shaft 33 is directed radially to the spherical faces and at an angle of 40-50 to the vertical axis of the digester. Each of said scraper means 35, 37 is of a length taking up an angle of 2535, as seen from the centre of the spherical faces, so that together they sweep great areas of the digester bottom and of the partition, respectively.

In order to further the passage of the pulp in the comparatively narrow necks without risk of clogging, there are provided devices for the dilution of the pulp, viz. a number of spray tubes 39, 41 for the supply of the dilution liquid, which tubes are distributed around the circumference of the digester. The spray tubes 4ll which have their orifices on the inside of the partition 23 close to its upper edge, extend radially across the interspace 25 and are attached to the partition 23 so that the latter is propped by said tubes and is securely held in its correct position truly concentric to the digester shell.

With the described eccentrical arrangement of the scraper devices the centre of the digester bottom will be left free so that space is provided there for other devices which may be of a stationary or moveable kind. The drawing shows a stationary central tube 43 extending into the digester through the neck 27. This tube can be used for supplying chips, digesting liquor or washing liquid to the digester. As an alternative, said tube may be rotary and carry agitators or spray nozzles.

What is claimed is:

1. In combination a cellulose digester having a shell with a cylindrical main portion and an approximately calotte-shaped bottom portion and a device for discharging cellulosic pulp from the lower end of the digester comprising a partition concentric t the digester shell and separating a central zone from a peripheral zone of the digester cross-section so that the space inside said partition communicates with a first pulp outlet and the space between the partition and the digester shell communicates with a second pulp outlet, s'aid partition being shaped approximately as a spherical calotte or zone concentric to the approximately calotte-shaped bottom portion of the digester, the upper part of the partition being propped by radially directed tubes for the supply of diluting liquid extending through the digester shell and partition for communication with the space inside said partition and at least three rotary scraper means inside the partition, each rotary scraper means being attached to a radially, outwardly and downwardly directed shaft which extends through the partition and the digester shell, said shaft also carrying scraper means in the space between the partition and the digester shell.

2. A cellulose digester comprising a shell having a cylindrical main portion and a substantially calotteshaped bottom portion, a partition located concentrically in the digester and having a calotte-shaped portion concentric to said digester shell bottom portion, the upper part of the partition being propped by radially directed tubes for the supply of diluting liquid extending through the digester shell and partition for communication with the space inside said calotteshaped partition, a first pulp outlet, a second pulp outlet, means connecting said first pulp outlet to the space inside said calotte-shaped partition, means connecting said second pulp outlet to the space between said partition and said digester shell bottom portion, at least three sets of scraper devices distributed around the circumference of the digester bottom, each of said sets comprising a drive shaft directed radially and at an acute angle to the axis of the digester and extending through said partition and through said digester shell bottom portion, scraper arms attached to said shaft in positions suitable for sweeping the inside of said calotte-shaped partition and forwarding pulp towards said first pulp outlet, and scraper arms attached to said shaft in positions suitable for sweeping the inside of said digester shell portion and forwarding pulp towards said second pulp outlet. 

1. In combination a cellulose digester having a shell with a cylindrical main portion and an approximately calotte-shaped bottom portion and a device for discharging cellulosic pulp from the lower end of the digester comprising a partition concentric to the digester shell and separating a central zone from a peripheral zone of the digester cross-section so that the space inside said partition communicates with a first pulp outlet and the space between the partition and the digester shell communicates with a second pulp outlet, said partition being shaped approximately as a spherical calotte or zone concentric to the approximately calotte-shaped bottom portion of the digester, the upper part of the partition being propped by radially directed tubes for the supply of diluting liquid extending through the digester shell and partition for communication with the space inside said partition and at least three rotary scraper means inside the partition, each rotary scraper means being attached to a radially, outwardly and downwardly directed shaft which extends through the partition and the digester shell, said shaft also carrying scraper means in the space between the partition and the digester shell.
 2. A cellulose digester comprising a shell having a cylindrical main portion and a substantially calotte-shaped bottom portion, a partition located concentrically in the digester and having a calotte-shaped portion concentric to said digester shell bottom portion, the upper part of the partition being propped by radially directed tubes for the supply of diluting liquid extending through the digester shell and partition for communication with the space inside said calotte-shaped partition, a first pulp outlet, a second pulp outlet, means connecting said first pulp outlet to the space inside said calotte-shaped partition, means connecting said second pulp outlet to the space between said partition and said digester shell bottom portion, at least three sets of scraper devices distributed around the circumference of the digester bottom, each of said sets comprising a drive shaft directed radially and at an acute angle to the axis of the digester and extending through said partition and through said digester shell bottom portion, scraper arms attached to said shaft in positions suitable for sweeping the inside of said calotte-shaped partition and forwarding pulp towards said first pulp outlet, and scraper arms attached to said shaft in positions suitable for sweeping the inside of said digester shell portion and forwarding pulp towards said second pulp outlet. 